Universal Serial Bus (USB) is an industry standard that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices.
The USB Specification, by the USB Implementers Forum, defines various high speed USB transactions, such as High Speed Bulk Transactions, High Speed Isochronous Transfers, High Speed Interrupt Transactions, High Speed Control Transfers, Split Transactions, Split Bulk OUT Transaction, Split Bulk IN Transaction, Periodic Split Transactions, Split Interrupt OUT Transaction, Split Interrupt IN Transaction, Split Isochronous OUT Transaction, and Split Isochronous IN Transaction. The various transactions operate according to various state machines, which in some cases are inadequate for USB extensions.